The present invention concerns an electronic timepiece concerning an oscillator used as a time base, a frequency divider with an adjustable division factor, which is coupled to the oscillator, a circuit for adjusting the division factor, a memory which is associated with the adjusting circuit and whose state represents the magnitude of said adjustment, and a transducer responsive to a signal generated in the timepiece by the emission of a wave which can be detected by an outside apparatus for measuring the rate of the timepiece.
For the purposes of measuring the rate of watches of this kind, use is made of devices which detect the magnetic stray field of the coil of the stepping motor, and which precisely measure the time which elapses between two drive pulses.
These devices rapidly give the required measured result when the drive pulses are separated by short periods of time, for example a second. On the other hand, in the case of watches which do not have second hands and in which the drive pulses may be spaced at from 10 to 20 seconds or even a minute, the rate measuring time is much longer.
U.S. Pat. No. 3,998,044 discloses apparatus which makes it possible to shorten the time required for measuring the rate of such watches, by supplying their motors with pulses which are produced by an intermediate stage of the frequency divider and which are sufficiently short for them not to cause the motor to react, while being of a sufficiently high frequency for the measuring time to be short. However this apparatus cannot be used for watches in which the frequency divider has an adjustable division factor. In such watches, which are described for example in Swiss Pat. Nos. 534,913 and 558,559, pulses are suppressed or added at certain positions in the division chain in the course of each adjustment cycle, which cycle may last up to 64 seconds. As a result of this, in the course of one of the adjustment cycles, the time between two successive drive pulses is not constant.
In order to be certain of correctly determining the rate of the watch, it is therefore necessary to compute the mean time which elapses between two drive pulses from the measured values of the time which elapses between each pulse appearing for a period of time which is at least equal to an adjustment cycle. The difficulty with such measurement operations is that nothing indicates the commencement or the end of an adjustment cycle.